10-nen mo 20-nen mo

Konashi is a hard-working swimming buff who's focused on becoming good enough to land himself a spot in the upcoming summer swim competition. One day while heading to the pool to swim as always, he spots a guy he's never seen before standing on the jumping board with his clothes and shoes still on. As it turns out he's Eguchi, the resident class "mystery" who's only ever attended one of his classes. As they get talking, Konashi realizes he's nothing like the rumours made him out to be and so began a quirky brief friendship that leaves a strong impression on him even years later. Source: MU Extra chapter from Baby Blue.